Alpine touring bindings allow the heel of the user's footwear (such as a ski boot) to be latched to a snow travel aid (such as a ski) for sliding downhill (the “downhill mode”) and allow the heel to be released for walking and climbing (the “touring mode”). Thus, the binding allows for selective holding of the footwear heel to the snow travel aid so that the user may select between the downhill mode and the touring mode. Modem alpine touring bindings allow the footwear to release from the snow travel aid when in the downhill mode, in case of a fall. When in the touring mode, the user may climb or walk with a great degree of freedom since the footwear is pivotally engaged with the aid near the toe of the footwear while the heel of the footwear is free to move upward and downward relative to the aid. A historical collection of such bindings can be viewed in the “Virtual Museum of Backcountry Skiing Bindings” at www.wildsnow.com, authored by Louis Dawson.
Alpine touring bindings sold under the brand DYNAFIT are bindings that take advantage of the fact that modern alpine touring boots have a rigid sole. Thus, it is unnecessary to provide a bar, plate or other arrangement connecting the toe and heel units, as is the case with many other alpine touring bindings (see patent publications EP0199098, EP0519243, EP1559457, and AT402020).
The DYNAFIT™ binding system comprises a toe unit which has a set of jaws that pivotally engage a special insert in the footwear sole. The toe unit is mountable at an appropriate location on the upper surface of a snow travel aid. A separate heel unit is mountable at a particular region on the upper surface rearward of the toe unit, the location of which is dictated by the length of the footwear sole. The toe and heel units function independently in retaining the footwear attached to the snow travel aid. The heel unit comprises projections (typically a pair of pins) which extend forward to engage opposite sides of a fitting placed over a cavity in the rear of the footwear heel. Under forward release conditions, the pins are intended to be forced apart against spring pressure to respective release positions to disengage from the fitting and the heel. The pins typically communicate with a spring or springs through inclined sliding surfaces that move a block which engages the spring or springs.
Fore and aft adjustment of the DYNAFIT™ heel unit to position the pins at an optimum depth in the heel fitting and to accommodate a limited range of different footwear sizes is provided by means of a threaded adjuster that moves a main portion of the heel unit relative to a base plate which is fixed to the upper surface of the snow travel aid. This is a fine adjustment that must be carried out by means of numerous rotations of a threaded adjuster, through the application of a tool such as a screwdriver or hex key.
The heel unit of a DYNAFIT™ binding provides lateral release primarily as a result of the body of the heel unit which contains the pins being pivotally engaged on a vertical post. Variable release settings are provided by adjusting compression of a spring that is internal to the body which forces a plunger against flat regions arranged on the post circumference.
To switch between touring and downhill modes with the DYNAFIT™ system, it is necessary to rotate the heel unit so that the pins either engage the footwear heel (downhill mode) or face away from the heel (touring mode). When the pins are facing away, the footwear heel is free to move upward and downward. A series of steps on the heel unit may also be provided which, upon rotation of the heel unit to different positions in the touring mode, allow the heel to be supported at varying heights above the snow travel aid to provide comfort during climbing. In order to switch from downhill mode to touring mode it is necessary to release the pins from the fitting on the heel such as by disengagement of the toe unit from the footwear, so that the footwear completely exits from the binding system whereupon the heel unit may be rotated to a position in the touring mode. A DYNAFIT™ type heel unit can also rotate on its own while in the tour mode, occasionally causing the heel unit to inadvertently switch to the downhill mode.
The snow brake for the DYNAFIT™ binding is positioned to not contact snow while in the touring mode by the user forcing the heel plate of the brake downwards while simultaneously rotating the heel unit to a position in the touring mode. This requires a manual activity on the part of the user, which can be difficult to accomplish while in deep snow or when poised in a precarious location.
A variation on a DYNAFIT™ type of binding is shown in WO 2009/105866 where the heel unit is adapted to translate forward and rearward, preferably by a single motion of an actuator to allow for engagement and disengagement of pins from the heel fitting without rotation of the heel unit. This allows the user to change the binding between downhill and touring modes while keeping the boot engaged with a toe piece. The type of binding illustrated in WO 2009/105866 does not rotate except during lateral release whereupon the binding returns to a normal position as a result of a biasing force exerted by lateral (Mz) release components of the binding. Also, translation forward and rearward of the binding in WO 2009/105866 may be used to change a ski brake from a stowed position for use in touring to a release position for use in downhill skiing whereby release of a boot from the binding in a fall will result in the snow brake being engaged with the snow surface.